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Full text of "Handbook Of Chemical Engineering - I"

6
CHEMICAL ENGINEERING
winter conditions. If heated all day and all night for six months, the annual heat consumption will than be 4,320 B.t.u. per cubic foot, corresponding with about 4.5 Ib. of steam. Some buildings require no heat. Where very slight heat is needed—as in a storehouse where it is merely desired to keep sprinkler pipes from freezing—the heat consumption is one-fourth to one-third this amount. Process Supply.—For heating W Ib. of any liquid from ti to Z2°F., the specific heat of the liquid being s, the heat required is Ws(tz — ti) B.t.u. For evaporating W Ib. of water, the heat required is WL B.t.u., where L is the latent heat of vaporization at the pressure under which evaporation occurs.
BOILERS
Types and Features.—Boilers may be classed as horizontal (Heine, locomotive) or vertical (Wickes, Manning); fire-tube (horizontal-tubular, Manning, locomotive) or water-tube (Babcock & Wilcox, Wickes, Stirling, Heine); exter-
FIG. 6.—Babcock & Wilcox boiler.
nally-fired (horizontal-tubular, Babcock & Wilcox) or internally-fired (locomotive, many marine). Internally-fired boilers (except some vertical types) are not commonly used in stationary practice. Large plants employ mostly the water-tube (approximately) horizontal form: Babcock & Wilcox, Heine, etc. Smaller plants often use horizontal tubular or vertical boilers (the latter sometimes internally fired).
Vertical boilers generally save floor space, but not if very large units are contemplated. Many such boilers have poor gas circulation and consequently are inefficient. Water-tube boilers may be shipped "knocked down." They usually contain less water, relatively, than fire-tube boilers and hence are safer as well as responsive more quickly to changes in load. Having no parts of large diameter, they are. the only boilers well adapted to high steam pressures. Highest rates of evaporation are realized on water-tube boilers.
Seams exposed to the fire are objectionable in all types.    The method of staying